The invention relates to surfaces coated with streptavidin/avidin. Fields of application of the invention are medical diagnostics and pharmaceutical industry.
To determine immunologically effective components according to the principle of the solid phase immunoassay where a reactant is bonded on a solid phase today usually reaction vessels in the form of tubes or wells of microtitration plates are used as solid phase on the inner surfaces of which or outer surfaces of pellets the reactant is bonded. It is the aim to coat these surfaces with organic chemical substances in a way as to reach highly specific bonds in the subsequent assay and to keep the number of non-specific bonds as small as possible.
In the last few decades the immunoassay in its multifarious forms has become established for the determination of a specific bondable immunological substance. It is possible to determine smallest substance quantities in the presence of a billionfold excess of foreign matter. The basis is the sensitive and specific competitive reaction of a non-marked substance P with a fixed quantity of a marked substance P* around specific bonding sites of a binding agent Q in a limited quantity. The concentration of the latter may be determined from the distribution pattern of the marked ligand as a function of the concentration of non-marked ligands. Various methods for separating converted from non-converted reactants have been developed.
In the last few years the solid phase method where one reactant is bonded on a solid phase gained major importance. Reactants bonded chemically or physically on the solid phase may be antibodies, antigens, receptors, cells, DNA, RNA etc. These reactants may be adsorbed on the solid phase either directly or through a precoating. Today it is usually modified with a specifically bondable substance, biotin, which allows to bond it on the coated supporting material (Patent DE 36 40 412 A1 and: Soukup, G. A. et al.: Bioconjugate Chemistry 6, 135/1995).
Today usually plastic surfaces of polystyrene, polypropylene, polyethylene, polyamide, polymethacrylate, polycarbonate, polyacrylate or copolymeres of polystyrene are used as supporting material in the form of inner surfaces of tubes or wells of microtitration plates or outer surfaces of pellets.
Various modifications of these surfaces are known. Thereby, the specifically bonding substance shall be bonded in a way as to make the bondage of the reactant modified by biotin stable, unaffected and sufficient for all manipulations required during the determination procedure. Here, the modified, specifically bonding reactant shall not lose its bondability. Today most of the coatings of solid phases are based on adsorptive bonds.
To ensure stability and an optimum coating adhering agents bringing about an adsorptive bonding were recommended. Here, there shall be made sure that the bondability of the specifically bonding reactant will not be affected (Patent DE 38 06 431).
The determination procedures so far known show the following drawbacks:
the adsorptive loading with reactants frequently results in a too low loading, PA1 a too low absorbancy of the coated surfaces for bonding the reactants subsequently biotinylated, PA1 high non-specific bonding occurring frequently, PA1 instability towards aggressive substances such as detergents, strong bases or acids.